The intensity of light that is provided in automobile tail lights, brake lights and turn indicator lights has generally been provided by supplying a D.C. current to the respective lamp, or more recently, to one of the respective filaments of the lamp. While this system has been used successfully in the past, there are several disadvantages including the need to run a separate wire to each lamp or filament therein increasing costs and decreasing reliability. Furthermore it is desirable to have a warning system to alert the operator of a lamp or wiring failure.
A solution to these problems is to combine the three signals into one signal that varies the intensity of light in the lamps by varying the duty cycle of the current driving the lamps. In this way, only one wire is required and a plurality of parallel lamps may be used to provide additional safety and reliability. The expected current and temperature could further be monitored to shut down the system and/or send a warning signal therein alerting the operator of a problem.
Thus, what is needed is a system in an automobile for combining several signals into one modulated signal for controlling the light intensity in a plurality of indicator lamps and for providing over-current and over-temperature protection.